Fuel gas for cutting operations

ABSTRACT

A FUEL GAS CONTAINING LOW MOLECULAR WEIGHT HYDROCARBONS AND BEING SUBSTANTIALLY FREE OF HYDROCARBONS CONTAINING MORE THAN 4 CARBON ATOMS AND INCLUDING PROPORTIONS, ON VOLUME BASES, OF METHYL ACETYLENE AND/OR ALLENE WITHIN THE RANGE OF FROM 5 TO 39%, PROPYLENE WITHIN THE RANGE OF FROM 30 TO 90%, AND PROPANE WITHIN THE RANGE OF FROM 0 TO 30%.

United States Patent 3,706,542 FUEL GAS FOR CUTTING OPERATIONS JamesHarris Gilks, Stockton-on-Tees, England, assignor to Imperial ChemicalIndustries Limited, London, England No Drawing. Filed Oct. 13, 1970,Ser. No. 80,470 Int. Cl. B23k 7/00; C] 3/00 US. Cl. 48-197 FM 5 ClaimsABSTRACT THE DISCLOSURE A fuel gas containing low molecular weighthydrocarbons and being substantially free of hydrocarbons containingmore than 4 carbon atoms and including proportions, on volume bases, ofmethyl acetylene and/or allene within the range of from 5 to 39%propylene within the range of from 30 to 90%, and propane within therange of from 0 to 30%.

This invention concerns fuel gases suitable for use in welding or torchcutting operations.

Currently, acetylene, and commercial propane which contains a variableproportion of propylene, are principal fuel gases for industrial cuttingoperations. For many purposes, either acetylene or commercial propanecan satisfactorily be used and the selection of one or other in giveninstances then turns more on considerations of cost, availability,equipment suitability, and, very often, the personal preference andexperience of the operators concerned. There are, however, otherimportant areas of operation where fundamental differences in theburning characteristics, including flame temperature and profile,require the use of one and not the other of these fuel gases; this isespecially the case with acetylene which realises a very high flametemperature and needs substantially less oxygen than propane for itscombustion.

Militating against even wider use of acetylene are its high productionand distribution costs which in part stem from the need for specialequipment and care in the storage and handling of what is intrinsicallya very hazardous material.

The present invention provides a cutting gas possessing substantialadvantages over propane in terms of flame temperature and profile andoxygen requirements but which can be safely stored, distributed andhandled broadly after the manner of commercial propane, that is to say,without the need for special packed cylinders and many other elaboratesafety measures which are a common feature of acetylene usage. It is,however, important that copper and phosphor bronze and related alloysshould be excluded from equipment in which the gas is used or stored.The fuel gas according to the present invention is a mixture containinglow molecular weight hydrocarbons and being substantially free ofhydrocarbons containing more than 4 carbon atoms and includingproportions, on volume bases, of methyl acetylene and/or allene withinthe range of from 5 to 39%, propylene within the range of from 30 to90%, and propane (if any) not exceeding 30%. It is preferred that therebe no substantial quantity of C hydrocarbons present. Thus, theproportion of C hydrocarbons should very desirably not exceed around 7%.Particularly important are compositions as so defined in which theproportion of methyl acetylene and/ or allene is at least and theproportion of propylene is at least 50%, the remainder being preferablyessentially propane or being propane and not more than 5% of Chydrocarbons. Thus, a typical preferred composition would essentiallyconsist of 20 to methyl acetylene/allene, 50 to 60% propylene and 15 to20% propane.

The invention further provides an improvement in processes for cutting,scarfing and brazing metal sheet, plate, pieces, or section, theimprovement consisting in using as the fuel gas instead, say, ofcommercial propane, a composition comprising methyl acetylene and/ orallene, propylene, and, optionally, propane as aforedescribed. Thecomposition is not suitable for welding materials requiring a reducingatmosphere. Principally envisaged are processes in which commercialpropane has heretofore been used although the use of the saidcomposition as a replacement for acetylene in many operations other thanwelding in which acetylene is now used is contemplated. Thus, otherapplications for the composition include soldering, flame hardening,flame spraying and descaling.

EXAMPLE 1 A cutting gas composition (mixture 1) was produced containing22% methyl acetylene/allene, 58% propylene, 18% propane and 2% Chydrocarbons.

EXAMPLE 2 A cutting gas composition (mixture 2) was produced containing15% methyl acetylene/allene, 70% propylene, and 15 propane.

EXAMPLE 3 A cutting gas composition (mixture 3) was produced containing10% methyl acetylene/allene, propylene and 5% propane.

The gases were tested for flame temperature properties and in metalcutting by standard industrial techniques and their performance wascompared with commercial propane containing propane and with acetylene.In the case of acetylene and propane, the equipment used was of standardoptimised design for these gases. In the case of the presentcompositions, suitable equipment was of course, designed for thecompositions having regard to their particular oxygen requirements andburning characteristics.

The following results were obtained in initial trials.

Length of cut per minute for mild steel plate of The quality of cut ineach case for mixtures 1, 2 and 3 was excellent.

In subsequent plant trials by operators who had acquired familiaritywith the present compositions outstanding performance was achieved.Thus, with a composition of the preferred make-up (as typified by thecomposition used in Example 1) 1 inch thick mild steel plate was cut ata rate of 70 feet per hour, and the finished was assessed as extremelygood.

Thus, a file rubbed along the face and bottom edge left a completelyclean material.

Other examples of important time savings and economies made possible bythe use of this composition were in the weld preparation time of steeltube (eg 12 inch diameter, 0.33 inch thick) and in the greatly increasedlife of tungsten carbide tipped cutting tools, the depth of hardnesspenetration being typically 0.038 inch at Brinell (cf. oxy-acetylenegiving hardness penetration of 0.104 inch at Brinell).

Additionally, high withdrawal rates from cylinders without the additionof vaporisers were found possible and the withdrawn gas was not found tovary to any detectable extent in composition throughout cylinder usage.There was no polymer formation and thus regulators and tool tips remainunclogged. The outstanding capability of preferred compositionsaccording to the invention was demonstrated by cutting through a feetthick 100 ton billet of steel. In general, also, brazing was found to beas fast or faster than with acetylene or mild steel, galvanised steel,copper, brass and aluminium. A typical set of physical and chemicalproperties for a preferred composition according to the invention is:

Liquid density33 to 35 lbs/ft. at 60 F.

Specific volume of gas9 to ft. /lb. at 60 F.

Net heat of combustion-2000 to 2500 B.t.u./lb. at 60 F. Vol. of 0 vol.of fuel for complete combustion-4 to 4.5. Flammability limits inair-2.2% to 11%.

Flame temperature-about 5500 F.

The working pressure of the fuel gas and oxygen will of course vary withthe job to be done but for many operations a fuel gas pressure in therange 3 to 10 p.s.i.g. and a corresponding oxygen pressure in the range35 to 90 p.s.i.g. will be suitable.

I claim:

1. A fuel gas composition for use in welding and torch cuttingconsisting essentially of from to of an unsaturated hydrocarbon selectedfrom the group consisting of methyl acetylene, allene and mixturesthereof, from to propylene and the balance being propane.

2. A fuel gas composition for use in welding and torch cuttingconsisting essentially of from 20% to 25% of unsaturated hydrocarbonselected from the group consisting of methyl acetylene, allene andmixtures thereof, from 50% to 60% propylene, up to 5% C hydrocarbons andthe balance being propane.

4 3. A fuel gas composition for use in welding and torch cuttingconsisting essentially of the following components:

Percent Methyl acetylene/allene 22 Propylene 58 Propane 18 Chydrocarbons 2 4. A fuel gas composition for use in welding and torchcutting consisting essentially of the following components:

Percent Methyl acetylene/allene 15 Propylene Propane 15 5. A fuel gascomposition for use in welding and torch cutting consisting essentiallyof the following components:

Percent Methyl acetylene/allene 10 Propylene Propane 5 References CitedUNITED STATES PATENTS 3,226,213 12/ 1965 Nelson et al 48-197 PM3,352,652 11/1967 Belfit, Jr. 48197 PM 3,337,314 8/ 1967 Belfit, Jr.48-197 FM 1'. SCOVRONEK, Primary Examiner US. Cl. X.-R.

